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8 Causes of Deep Vein Thrombosis

Obesity, older age, and even long-distance travel can increase the risk of deep vein thrombosis (DVT), a potentially life-threatening type of blood clot.

When you get a cut or scrape, your blood clots to stop the bleeding, and that’s a good thing. But sometimes blood clots form in large veins deep in your body, typically in the legs or thighs. Rather than being helpful, these clots can be a serious health problem.

This kind of blood clot is known as deep vein thrombosis (DVT). A blood clot in a vein deep in the body is made up of platelets, which speed the clotting process, and fibrin, a protein that weaves a web to trap blood cells. The real danger develops if a piece of the clot breaks off, travels through the bloodstream, and lodges in the lung, says Nieca Goldberg, MD, a cardiologist and the medical director of the Joan H. Tisch Center for Women's Health at the NYU Langone Medical Center in New York City. This is called a pulmonary embolism (PE), which can be life-threatening, she says.

According to the Centers for Disease Control and Prevention, every year, between 300,000 and 600,000 Americans have DVT or PE.

What Causes DVT?

Anyone can develop DVT, but some people are at greater risk than others. These situations can raise your risk:

Injuring a vein. Injury to a vein can occur from breaking a bone or severely damaging a muscle. Veins can also be injured during major surgery, especially if the procedure involves the pelvis, hips, or legs.

Being immobile. If you keep your legs still for an extended period of time — maybe because you’re wearing a cast, recovering from surgery, or even taking a long-distance flight or car trip, for example — your blood flow slows. This can prevent anti-clotting agents in the body from mixing properly in your blood.

Taking hormones. If you're a woman and take certain types of birth control pills or hormone replacement therapy (HRT) after menopause, you may be at higher risk of DVT, says Shahrzad Shareghi, MD, a cardiologist at Los Robles Hospital in Thousand Oaks, Calif. That’s because the hormone estrogen, which is present in some forms of birth control and HRT, may cause the blood to clot more easily. “If you take birth control pills or HRT and you smoke, you are at an even higher risk,” she says.

Being pregnant. Pregnancy increases a woman’s risk of DVT, and the risk from pregnancy remains higher up to six weeks after delivery, Dr. Shareghi says. Similar to taking hormones, the risk is related to the increase in estrogen when a woman is pregnant, as well as a function of the body that helps prevent women from experiencing too much blood loss during childbirth.

Having cancer. Cancer raises the risk of DVT. “When cancer forms, it sets off clotting reactions that make a person more prone to forming clots,” says Larry Santora, MD, a cardiologist at St. Joseph Health in Orange, Calif. “The danger is mostly with cancers of the abdomen and pelvis, but any kind of cancer can increase the risk of DVT.”

Having other health conditions. Chronic health problems that raise the risk of DVT include heart disease, lung disease, and inflammatory bowel diseases such as Crohn’s disease and ulcerative colitis. People who have clotting disorders are also at greater risk of DVT.

Having a history of DVT. Once you have DVT or a PE, your risk for another episode is higher, Dr. Goldberg says. Also, if anyone in your family has a history of DVT or PE, this increases your risk as well.

Being older or overweight. Your risk of DVT increases with age, particularly for those older than 75. It’s hard to say whether that’s because your veins and blood flow weaken or because you move less as you get older, Shareghi says. And obesity is yet another DVT risk factor, the Society of Interventional Radiology reports.

Know the Signs and Symptoms of DVT

It’s important to recognize the signs and symptoms of DVT because early treatment can save your life. If your leg swells, feels tender or painful, or is red and warm, seek medical attention immediately. An ultrasound of your leg will show if you have DVT. If so, treatment with blood thinners can dissolve the clot and prevent it from getting bigger. If DVT is severe, you may need surgery to remove the blood clot.

Left alone, DVT can lead to PE and potentially death. According to the Society of Interventional Radiology, of every 100 people who develop DVT, one will die of PE. Get medical care right away if you notice any signs or symptoms of DVT, and talk to your doctor if you’re concerned about your risk.